Mechanical heart pumps are typically external devices temporarily used when a patient is undergoing surgery to repair the heart or to transplant another heart. Mechanical pumps to be implanted are also known but not in extensive use because of the technical problems to be solved. If used for an extended time, the pump ideally should duplicate the human heart. The human heart has a pulse and operates at different blood pressure levels depending upon the type of exertion of the patient. A patient's arteries and veins will naturally expand during exertion, which tends to lower the blood pressure. The patient's arteries and veins will contract while the patient is sedentary, increasing the blood pressure back to an at rest level. Also, while the patient is exercising, in addition to the pulse rate being higher, each stroke of the human heart will pump more blood than while the patient is sedentary.
Rotary heart pumps cannot duplicate a pulse. While reciprocating heart pumps are known, they normally are configured to pump the same volume of blood with each stroke. While workable, changes in blood pressure caused by exertion of the patient are detrimental to the check valves and other components of the pump chamber if the same volume of fluid is pumped with each stroke. Consequently, known reciprocating type heart pumps must be replaced at fairly frequent intervals.